1. Field of the Invention
This invention relates to machines for packaging free flowing solid materials, such for example as tea, of the type comprising a rotary dispensing drum having in its periphery a row of circumferentially spaced pockets, a feed hopper to contain the material to be packaged which is disposed above the drum and has an outlet at its lower end through which the material flows by gravity into successive pockets in the drum as the drum rotates, means for feeding a lower web of packaging material into contact with the periphery of the drum so that it covers the filled pockets and leaves the bottom of the drum in a substantially horizontal run carrying spaced piles of material deposited on the web from successive pockets in the drum, and means for superposing an upper web of packaging material on the lower web to cover the piles of material and sealing the webs together around the perimeter of each pile.
2. Description of the Prior Art
Machines of this type are described in British Patent Specification No. 938,337 (FIG. 4) and in U.S. Pat. No. 2,746,223 and are in commercial use for the production of tea bags.
During a production run of such a machine for producing tea bags there are inevitably changes during the run in the density of the tea being packaged. Since the weight of tea in the bags must remain constant this necessitates a compensating adjustment of the machine while it is running.
Hitherto such adjustment has been by means of plungers which are movable in unison into and out of the pockets to vary the volume of the pockets by an adjustment made by the machine operator whenever check weighing of the bags shows that such adjustment is necessary.
This procedure has two disadvantages. Firstly the mechanism required, which involves simultaneous and equal adjustment of the volume of all of the pockets while the machine is running, is extremely complex and expensive. Secondly the mechanism imposes a serious restriction on the speed at which the machine can be operated for the following reason.
When a plunger is advanced into a pocket to reduce its volume, each pile of tea deposited on the lower web has a crater at the top and the annular rim surrounding the crater is easily disturbed, if it is sought to run the machine at high speed, causing the tea to spread from the designated pile area into the zone at which the surrounding seal is to be made between the webs. Penetration of tea into this zone results in incomplete sealing and leakage of tea from the bags.